drm/i915: Tweaked Wa_14010685332 for PCHs used on gen11 platforms

drm/i915: Tweaked Wa_14010685332 for PCHs used on gen11 platforms

The WA specifies that we need to toggle a SDE chicken bit on and then
off as the final step in preparation for s0ix entry.

    Bspec: 33450
    Bspec: 8402

However, something is happening after we toggle the bit that causes
the WA to be invalidated. This makes dispcnlunit1_cp_xosc_clkreq
active being already in s0ix state i.e SLP_S0 counter incremented.
Tweaking the Wa_14010685332 by setting the bit on suspend and clearing
it on resume turns down the dispcnlunit1_cp_xosc_clkreq.
B.Spec has Documented this tweaked sequence of WA as an alternative.
Let keep this tweaked WA for Gen11 platforms and keep untweaked WA for
other platforms which never observed this issue.

v2 (MattR):
 - Change the comment on the workaround to give PCH names rather than
   platform names.  Although the bspec is setup to list workarounds by
   platform, the hardware team has confirmed that the actual issue being
   worked around here is something that was introduced back in the
   Cannon Lake PCH and carried forward to subsequent PCH's.
 - Extend the untweaked version of the workaround to include  PCH_CNP as
   well.  Note that since PCH_CNP is used to represent CMP, this will
   apply on CML and some variants of RKL too.
 - Cap the untweaked version of the workaround so that it won't apply to
   "fake" PCH's (i.e., DG1).  The issue we're working around really is
   an issue in the PCH itself, not the South Display, so it shouldn't
   apply when there isn't a real PCH.

v3:
 - use intel_de_rmw(). [Rodrigo]

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Bob Paauwe <bob.j.paauwe@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201110121700.4338-1-anshuman.gupta@intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>